1. Field of the Invention
The present invention relates to a printing system that has print heads equipped with a plurality of nozzles arrayed crossing the scanning direction of a carriage in the carriage and forms successive scanning print areas by repeating feed of a printing medium to the direction orthogonal to the scanning direction and scanning by the carriage, and a printing information processing system that provides printing signals to the printing system, and in particular to a technology to perform printing with correction of the ink density in the predetermined boundary areas in the vertically adjacent scanning print areas.
2. Description of the Related Art
As image printing systems that print images on printing media such as paper and OHP (Over Head Projector) sheets, a number of systems have been proposed that are equipped with print heads using a variety of printing methods. Those print heads use printing methods including, for example, wire-dot method, heat-sensitive method, heat-transfer method and ink-jet method. In particular, among them the ink-jet method, where printing is carried out by ejecting ink directly on printing media, has drawn attention as an excellent printing method for lower running costs and a quiet printing operation.
The above printing systems are equipped with scanning carriages that have print heads and move horizontally. In each of these types of printers equipped with a scanning carriage, a number of nozzles mounted on the print head are driven by printing information during scans by the carriage, and after printing has been completed over one scanning print area, the printing medium is forwarded vertically to the direction the carriage proceeds as much as one scanning print area. This scanning motion of the carriage and the forwarding of the print medium create predetermined images.
If the fed printing medium or paper has stopped at a location slightly departed from the right location because of, for example, friction and problems in the feeding mechanism, the bottom of the printed area overlaps the top of the following printed area. As a result, there will be deterioration in image printing quality because the ink condensed in the overlapped trail appears as what is called a black stripe. To cope with this problem, a number of measures to improve the precision of the paper feed mechanism have been proposed.
However, if the printing medium is, for example, normal paper where ink spreads easily, there still appears a black stripe in the boundary area between the bottom of the preceding printed area and the top of the subsequent printed area, even though the paper has been precisely located in the right position. Although the detail of its mechanism is not clear, it is probable that when ink is ejected on paper the osmosis of the printed area therein is enhanced and then the ejected ink on the subsequent area spreads into this adjacent printed area.
As a solution to this problem, a head shading method is disclosed in Japanese Patent Application Laid-open No. 5-220977 (1993) where the ink density fluctuation and black stripes will be eliminated by adjusting the density of each raster of the original image.
The above conventional technology, however, has the following problems.
The technology revealed in Japanese Patent Application Laid-open No. 5-220977 (1993) provides a density correction for the upper or lower nozzles on the print head. By this technology, however, it is impossible to detect ink smears caused by the overlap of two or more colorants, when printing is performed by two or more print heads as is the case with color ink-jet printing systems. This technology, therefore, cannot eliminate black stripes that appear in full-color images.
In order to prevent ink smears, what is called a two-path printing method has been carried out where the image of one scanning print area is created by two scans of the carriage, with the printed paper being forwarded in the direction the paper is fed as long as half the full forwarding range. This method, in turn, has another problem that the printing speed becomes significantly low, while smears can be eliminated.
The purpose of this invention is to provide a printing method and printing system that can eliminate the black stripe in the boundary area and provide an excellent printing speed when full-color images are created by a plurality of print heads.
In a first aspect of the present invention, there is provided a printing information processing apparatus providing printing signals to a printing apparatus which has a plurality of print heads in a carriage, each of the heads being comprised of an array of printing elements, the carriage and a predetermined printing medium being relatively moved to the primary scanning direction and a sub-scanning direction orthogonal to the primary scanning direction respectively, and by the use of the printing elements forms scanning print areas adjacent to each other sequentially along the sub-scanning direction based on printing signals during the carriage movement over the printing medium to the primary scanning direction, the printing information processing apparatus comprising:
means for calculating a total value of printing signals sent to each of the print heads for printing onto at least one of upper or lower adjacent boundary areas in upper and lower adjacent scanning print areas formed by the print heads; and
means for correcting the printing signals for at least one of the upper and lower adjacent boundary areas, based on the total value of printing signals.
In a second aspect of the present invention, there is provided a printing apparatus comprising a plurality of print heads comprised of an array of printing elements, a carriage holding the print heads and shuttling along a primary scanning direction, means for moving a printing medium to a sub-scanning direction orthogonal to the primary scanning direction, and means for controlling the print heads equipped with the printing elements based on printing signals,
wherein the carriage moves in the primary scanning direction, the printing medium moves in the sub-scanning direction, and a plurality of scanning print areas are formed sequentially along the sub-scanning direction based on printing signals during the carriage movement, and
the means for controlling the print heads comprising:
means for calculating the total value of printing signals sent to each of the print heads, the printing signals for printing onto at least one of upper or lower adjacent boundary areas in upper and lower adjacent scanning print areas formed by the print heads,
means for correcting printing signals for at least one of the upper and lower adjacent boundary areas, based on the total value of printing signals calculated by the calculation, and
a printing element control unit that controls each of the printing devices of the print heads based on the printing signals corrected by the means for correcting printing signals.
In a third aspect of the present invention, there is provided a printing information processing method in which printing signals are provided to a printing apparatus which has a plurality of print heads in a carriage, each of the heads being comprised of an array of printing elements, the carriage and a printing medium being relatively moved along the primary scanning direction and the sub-scanning direction orthogonal to the primary scanning direction, respectively, and by means of the printing elements forms scanning print areas adjacent to each other sequentially along the sub-scanning direction based on the printing signals during the carriage movement over the printing medium along the primary scanning direction, each of the scanning print areas having the same length as that of the array of the printing elements measured in the sub-scanning direction;
the printing information processing method comprising the steps of:
calculating a total value of printing signals sent to each of the print heads for printing with respect to at least one of upper or lower adjacent boundary areas in upper and lower adjacent scanning print areas formed by the print heads; and
correcting the printing signals of at least one of the upper and lower adjacent boundary areas, based on the total value of printing signals.
In a fourth aspect of the present invention, there is provided a printing method in which printing signals are provided to a printing apparatus which has a plurality of print heads in a carriage, each of the heads being comprised of an array of printing elements, the carriage and a predetermined printing medium being relatively moved along a primary scanning direction and a sub-scanning direction orthogonal to the primary scanning direction respectively, and by means of the printing elements forms scanning print areas adjacent to each other sequentially along the sub-scanning direction based on printing signals during the carriage movement over the printing medium to the primary scanning direction;
the printing method comprising the steps of:
controlling each of the printing elements of the print heads based on the printing signals corrected by the correction step,
calculating the total value of printing signals sent to each of the print heads for printing with respect to at least one of upper or lower adjacent boundary areas in upper and lower adjacent scanning print areas formed by the print heads; and
correcting the printing signals of at least one of the upper and lower adjacent boundary areas, corresponding to a magnitude of the total value of printing signals.
In the present invention, because the total value of printing signals for the boundary area is calculated to control the printing signals thereof, the printing in the boundary area is always performed with an appropriate amount of ink, and emergence of black stripes can be prevented. That is, in the case of color printing conducted with a high ink density, if a significant amount of ink is ejected from the print heads of different colors, the ejected ink will spread in a wide range with high density to the boundary area where two scanning areas are adjacent to each other, and as a result, it is very probable that a black stripe appears in the boundary area. In the present invention, however, since the value of printing signals sent to each print head is calculated and this value is corrected to reduce the printing signals for the boundary area if it exceeds a predetermined threshold value, excessive supply of ink to the boundary area is prevented. Then the spread of ink is minimized and thereby emergence of a black stripe is prevented in advance. Further, the present invention allows high-speed printing because printed areas are sequentially formed by the full forwarding of each printed area scanned by the print heads.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.